Amphibian responses to wetland restoration in the Lower Mississippi Valley, USA

Background/Question/Methods

Agricultural cultivation is a major contributor to wetland loss and alteration and may impact wetland-dependent species such as many aquatic-breeding amphibians. Historically, the Lower Mississippi Valley (LMV) was the largest bottomland hardwood forest (BLH) ecosystem in North America and provided extensive wetland habitat for many species.  Today, only 20% of the original BLH remains.  The U.S. Department of Agriculture (USDA) Natural Resources Conservation Service has launched the Conservation Effects Assessment Program (CEAP), designed to restore wetland functions and services and thereby quantify the environmental benefits of conservation practices used by private landowners participating in USDA conservation programs.  As part of the CEAP Wetlands assessment, we measured amphibian habitat use within the LMV for 16 randomly selected sites that were (1) cultivated in cropland (agriculture), (2) formerly croplands restored through the Wetland Reserve Program (WRP), and (3) mature bottomland hardwood forest (total of 48 sites). We used automated digital recorders (ARU’s) to record the number of species of calling male anuran amphibians from April to June 2007 at each site.  We estimated probabilities of detection and site occupancy within each land use category using a single-season Bayesian hierarchical model of community species occurrence. 

Results/Conclusions

This model simultaneously estimated parameters for each of 11 species we detected and was then used to derive an estimate of species richness of the amphibian community at each site. Overall, there was a trend toward an increasing estimated number of species per site for WRP and forested sites, compared to agricultural sites.  Species-specific estimates of probabilities of occurrence varied among species and land-use categories.  Relative to agricultural sites, 8 of 11 species were significantly more likely to occur at WRP sites and 6 were significantly more likely to occur in forested sites.  Five of these latter species had similar estimates of occurrence in WRP and forested sites, suggesting that patches undergoing restoration may be an important transitional habitat for species that prefer sites with an open canopy, vertical vegetational structure, and habitat heterogeneity.  Thus, WRP conservation practices may restore suitable habitat and reduce the impact of agriculture-induced habitat loss on amphibian populations.